__init__(self)(Constructor)

'function' - a scanner function taking two or three
arguments and returning a list of strings.

'name' - a name for identifying this scanner object.

'argument' - an optional argument that, if specified, will be
passed to both the scanner function and the path_function.

'skeys' - an optional list argument that can be used to determine
which scanner should be used for a given Node. In the case of File
nodes, for example, the 'skeys' would be file suffixes.

'path_function' - a function that takes four or five arguments
(a construction environment, Node for the directory containing
the SConscript file that defined the primary target, list of
target nodes, list of source nodes, and optional argument for
this instance) and returns a tuple of the directories that can
be searched for implicit dependency files. May also return a
callable() which is called with no args and returns the tuple
(supporting Bindable class).

'node_class' - the class of Nodes which this scan will return.
If node_class is None, then this scanner will not enforce any
Node conversion and will return the raw results from the
underlying scanner function.

'node_factory' - the factory function to be called to translate
the raw results returned by the scanner function into the
expected node_class objects.

'scan_check' - a function to be called to first check whether
this node really needs to be scanned.

'recursive' - specifies that this scanner should be invoked
recursively on all of the implicit dependencies it returns
(the canonical example being #include lines in C source files).
May be a callable, which will be called to filter the list
of nodes found to select a subset for recursive scanning
(the canonical example being only recursively scanning
subdirectories within a directory).

The scanner function's first argument will be a Node that should
be scanned for dependencies, the second argument will be an
Environment object, the third argument will be the tuple of paths
returned by the path_function, and the fourth argument will be
the value passed into 'argument', and the returned list should
contain the Nodes for all the direct dependencies of the file.